DNS single-source Phase 1 + decommission Tailscale fleet-wide

Phase 1 of the DNS-redundancy cleanup (keep NetBird, collapse toward one
zone) — the safe, mesh-independent half:

- Every homelab LXC now resolves via Technitium (192.168.8.2). Fixed 8
  boxes on a dead resolver (.180), the router (.1), or Tailscale MagicDNS
  (100.100.100.100): 101,102,104,105,106,114,119,126.
- Removed the redundant /etc/hosts auth/mcp/secrets overrides (Technitium
  returns identical-or-better answers); disabled hubris-hosts-override.
- Net effect: on-prem DNS (LXCs + household via Fritz!Box->Technitium) is
  now NetBird-independent, so dropping the managed zone later can't break
  on-LAN resolution. Phases 2-4 still pending.

Tailscale decommissioned (was legacy/being-phased-out):
- Removed from the 6 LXCs still running it (101,103,104,105,114,119):
  logout, disable tailscaled, apt purge, state cleared.
- inventory.yaml: dropped tailscale from accepted + all mesh blocks;
  regenerated hosts/*.yaml (also pruned orphan authentik/claudio-bot).
- Tightened secrets-issuance MESH_SUBNETS: removed the now-vestigial
  Tailscale CGNAT range 100.64.0.0/10.
- Updated narrative docs (mesh, dns, network, README, AGENTS,
  agent-enrollment, homelab-context, 105-apps, 107-dns).

Live infra changed on the fleet + Mac; this commit records the docs/inventory.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

AGENTS.md

@@ -19,8 +19,8 @@ the operator to run `homelab client add <hostname>` from an existing client.
 - `/opt/homelab-context/inventory.yaml` — every host, LXC, VM, and workstation
   with their mesh addresses, roles, and service mappings. Treat this file as
   authoritative; anything you read in narrative pages should agree with it.
-- `/opt/homelab-context/infrastructure/mesh.md` — Tailscale → Netbird state.
-  Both meshes are accepted today; Netbird is preferred for new traffic.
+- `/opt/homelab-context/infrastructure/mesh.md` — Netbird mesh state.
+  Tailscale was decommissioned 2026-06-21; the fleet is Netbird-only.
 - `/opt/homelab-context/infrastructure/dns.md` — split-horizon DNS via
   dnsmasq on LXC 124. `*.hubris.network` resolves to 192.168.x.x on the LAN
   and to mesh addresses off-LAN.